docs: def check_roundoff(self, rtol=0.25, atol=1e-6):
          """ Check for roundoff errors in fit.p.
  
          Compares standard deviations from fit.p and fit.palt to see if they
          agree to within relative tolerance ``rtol`` and absolute tolerance
          ``atol``. Generates a warning if they do not (in which
          case an SVD cut might be advisable).
          """
          psdev = _gvar.sdev(self.p.flat)
          paltsdev = _gvar.sdev(self.palt.flat)
          if not numpy.allclose(psdev, paltsdev, rtol=rtol, atol=atol):
              warnings.warn("Possible roundoff errors in fit.p; try svd cut.")